1. Technical Field
The present invention relates to a printer that can print to paper of different widths, and to a control method for the printer.
2. Related Art
A reference position for loading the paper is commonly set in printers that print using a print head that is mounted on a carriage and travels widthwise to the paper. This reference position may be a left-edge reference (or right-edge reference, here and below) for positioning the left edge of the paper to the left side (or right side, here and below) of the paper transportation path, or it may be a center reference for positioning the paper in the center of the paper transportation path. When a left-edge reference is used and the left margin is constant, the start printing position of the print head is the home position of the print head (the left end of the range of print head movement) or a position at a constant distance from the left side of the paper transportation path. This configuration has the advantage of not needing to adjust the start printing position of the print head when the paper width changes, and enables printing to always start from the same position (start printing position).
If a center reference is used, however, the start printing position of the print head must be adjusted when the paper width changes even if the margin at the left side of the printing area remains the same because the position where the print head starts printing shifts widthwise to the paper. Therefore, in order to print accurately within the printing area of the paper, information such as the paper width or the positions of both the left and right edges of the paper are required in addition to the size of the left margin at the left side of the printing area.
In the case of a printer in which roll paper is loaded for printing, however, the balance will shift if a heavy roll of paper is set to the left or right side of the roll paper compartment. Setting the roll paper in the center of the roll paper compartment has the advantage of facilitating loading the roll paper and improved operational stability during printing. More particularly, because setting the roll paper in the center of the roll paper compartment affords more space and avoids the sides of the roll paper compartment where it can be difficult to reach by hand, the ease of loading the paper is improved. Paper transportation stability is also improved because the paper is not set to an unbalanced position on the left or right side. When the roll paper is loaded in the center of the roll paper compartment, the paper pulled off the roll is also positioned to the center reference of the transportation path. This makes adjusting the start printing position according to the width of the paper necessary as described above, and requires information about the paper width or the positions of the left and right edges of the paper.
Japanese Unexamined Patent Appl. Pub. JP-A-H10-16345 teaches a printer that detects the left and right edges of the paper and adjusts the start printing position of the print head. The printer taught in JP-A-H10-16345 detects the left edge and right edge of the paper by a paper sensor mounted on the carriage. If the position of the detected left edge is at the reference position, this printer prints without adjusting the start printing position, but if the position of the left edge is not at the reference position, the start printing position of the print head is adjusted for printing according to the position of the detected left edge. The start printing position of the print head can thus be automatically adjusted.
A problem with the method of detecting the paper edge each time by a paper sensor as taught in JP-A-H10-16345, however, is that processing by the printer becomes time consuming.
One conceivable solution is for the host device to send such information as the paper width or the reference position of the paper used for printing to the printer, thereby enabling the printer to acquire the necessary information and adjust the start printing position of the print head without executing a detection operation using a paper sensor.
However, generating the paper width or reference position information on the host device side and sending this information to the printer for each print job increases the processing load on the host device side while also requiring processing time on the printer side. When the paper width does not change, or there is a left-edge reference or right-edge reference that remains a constant reference printing position, it is preferable for the host device to not need to generate and send this information to the printer and the printer to not need to receive and process the information.